1. Field of the Invention
The invention relates to roofing flashing. More particularly, the invention relates to a flashing system for a plumbing stack vent pipe.
2. State of the Art
Vent pipes are typically provided in roofs of residential buildings to permit the escape of gas-phase materials. Indeed, most residential building codes require that building's sewer connections be provided with vents so that obnoxious and potentially hazardous fumes are not released into the building. These connections are typically achieved by extending a pipe through the roof so that it opens upwardly to the sky. A seal is placed around the outside of the pipe where it passes through the roof to prevent rainwater or other precipitation from entering the building. However, no provision is made to prevent rainwater from entering the pipe itself, the assumption being that since the pipe is connected to the sewage system, little harm is done in permitting leakage into the pipe.
A common boot-type flashing for sealing the space surrounding a vent pipe is disclosed in U.S. Pat. No. 3,313,559. The flashing consists of a sheet of aluminum or steel with a central opening sized to allow a vent pipe to pass through it, and a frustoconical rubber gasket which seals the space between the pipe and the sheet. The prior art vent pipe flashing works reasonably well most of the time. However, leaks can and do occur in these types of seals when the rubber gasket becomes loose.